Oracle7 Server Concepts

An Introduction to the Data Dictionary

One of the most important parts of an Oracle database is its data dictionary. The data dictionary is a read-only set of tables that provides information about its associated database. For example, a data dictionary can provide the following information:

the names of Oracle users

privileges and roles each user has been granted

names of schema objects (tables, views, snapshots, indexes, clusters, synonyms, sequences, procedures, functions, packages, triggers, and so on)

information about integrity constraints

default values for columns

how much space has been allocated for, and is currently used by, the objects in a database

auditing information, such as who has accessed or updated various objects

in Trusted Oracle, the labels of all objects and users (See the Trusted Oracle7 Server Administrator's Guide

other general database information

The data dictionary is structured in tables and views, just like other database data. To access the data dictionary, you use SQL. Because the data dictionary is read-only, users can issue only queries (SELECT statements) against the tables and views of the data dictionary.